Character display tubes



Feb 7, l967 G. F. KLEPP ETAL 3,303,375

CHARACTER DI SPLAY TUBES Filed July 16, 1965 2 Sheets-Sheet l 5 @l ff Ll] ff Inventors GEORGE F. KLEPP OAF H. ALTON BycAsnw A off/vaca Feb. 7, 1967 G. F. KLEPP ETAL CHARACTER DISPLAY TUBES 2 Sheets-Sheet 2 Filed July 16, 1953 Inventors GERGE F. KLEPP @LAF DALTIV cAsro/v A' aefffA/Ga UnitedStates Patent O 3,303,375 CHARACTER DISPLAY TUBES George F. Klepp, (Maf H. Dalton, and Gaston Pakenham de Mengel, London, England, assignors to International Standard, Electric Corporation, New York, N.Y., a corporation of Delaware Filed July 16, 1963, Ser. No. 295,333 Claims priority, application Great Britain, July 26, 1962, 28,770/ 62 1 Claim. (Cl. 313-1095) The present invention relates to electric glow discharge tubes, having an anode and a plurality of cathodes.

In the construction of electric glow discharge tubes there exists the problem of ensuring that cathode glow does not occur at leads to the cathode electrodes. To prevent this the leads may be coated with insulating material, such as alumina, which, however, tends to ake ot or become coated with cathode material due to sputtering. Alternatively the leads may be completely shrouded by insulating tubes; these have usually to be loosely tting and are allowed a limited degree of longitudinal movement along the leads, in consequence of which they may rattle when in transit and cause customers to think that the tube is detective; furthermore adequate shrouding is diiiicult to achieve and tends to be expensive.

According to the present invention a gas filled glow discharge tube is provided having an anode and a plurality of cathode electrodes wherein bare leads to cathode electrodes are spaced between a first and a second structural member of the tube, one of the members being electrically conductive, and wherein the spacing between the leads and each of the two members is less than the minimum sparking distance between them and an anode electrode in the same gaseous atmosphere.

In an indicator glow discharge tube according to the invention there is provided a glass envelope with a base at one end and, at the top end, a transparent part to permit viewing of glow discharge display within the tube, the base having lead pins sealed therethrough, and an electrode assembly supported by one or more of the lead pins, the electrode assembly including a metal cup with its base adjacent the base of the envelope, a plurality of spaced apart stacks of ceramic collars Within the cup extending adjacent the cup side walls from the base of the cup towards the top end of the envelope, an aperture through the base of the cup being provided between each stack and the immediately adjacent side wall of the cup, a set of cathodes each shaped for example as a diierent numeral with a pair of projecting ears and mounted by its ears being held between respective pairs ofthe ceramic collars so that the various cathodes lie in respective superimposed planes, and an anode member in the form of a metal mesh extending substantially to the rim of the metal cup over the set of cathodes, an electrical connection between a said lead pin and the metal cup, and an electrical connection between the said anode member and the cup or another lead pin, an electrical lead to each cathode from a respective lead pin to an ear of the cathde, each electrical lead to a cathode being taken through a said aperture in the base of the metal cup and being disposed, from its connection with its cathode ear to its passage through the base of the metal cup, ybetween the adjacent stack of ceramic collars and the cup side wall, the envelope being lled with a gas at such pressure and the electrode spacings being such that, for a specirice ed discharge current at a specied potential diierence applied between the said anode and any one of the cathodes, the metal cup being at the anode potential, glow discharge as seen through the top end of the envelope appears to cover substantially the whole cathode surface facing the top end, the arrangement of the electrical leads and of the .ceramic collars being such that the collars effectively shield the cathode ears to prevent glow discharge thereon and the .spacing of each lead from its adjacent stack of ceramic collars on the one side and the side wall of the metal cup on the other being too small to permit glow discharge at the lead in question being started or maintained when the said s pecitied voltage exists between it and the metal cup.

An embodiment of the invention will be described with reference to the accompanying drawings, in which:

FIG. l is a perspective view of an indicator tube according to the invention with parts broken away to show the general construction;

FIG. 2 is a side view of part of the electrode assembly of the tube of FIG. 1; and

FIG. 3 is a plan view of the assembly, the cathodes being omitted to simplify the drawing.

In the embodiment of FIG. 1 a glass envelope 1 has at one end a base 2 carrying lead pins 3 sealed through it and, at the other end, a transparent part 4, through which glow discharge display within the tube may be seen. An electrode assembly 5 is mounted on selected ones of the lead pins 3. The assembly 5 includes a generally cylindrical metal cup 6 having a base 7 mounted above and adjacent the envelope base 2 and electrically shielded from it by means of a mica disc 8, which, as shown better in FIG. 2, is somewhat larger than the base of the cup. Within the cup adjacent the side walls and extending from the base of the cup towards a viewing window 4, are located a plurality of spaced apart stacks of ceramic collars 9; in FIGS. 1 and 3 two such stacks are shown but more may be provided if desired. The collars are threaded over a metal rod 10 (FIG. 2) which passes through the base of the cup and is joined to one of the lead pins 3. The lowest collar may pass through a close tting aperture in the base of the metal cup and rest upon the mica washer 8, but, in any case, this aperture or a neighbouring one is extended to the rim 0f the cup to afford passage for electrical leads to the electrodes through the base of the cup. The stacks of ceramic collars support a set of cathodes 11 each shaped for example, in the form of a dilierent numeral, a set of numerals 1 to 9 and 0 normally being provided. Each cathode is provided with a pair of projecting ears clamped between respective pairs of ceramic collars on the stacks, the arrangement being such that the numerals lie each in respective superimposed parallel planes below the top end of the tube. The relative sizes of the ceramic collars and the ears are such that the ears are substantially shrouded by the collars so that glow discharge to the ears is prevented. Au anode member in the form of a metal mesh 12 extends over the set of cathodes substantially to the rim of the cup. The mesh may be supported between pairs of ceramic washers at the top of the stacks 9 or may be welded to the metal cup.

In FIG. l an additional anode mesh 12a is shown inserted transversely across the set of cathodes about half way up from the base of the cup, but in other embodiments this second anode mesh may be omitted or take some other form than mesh such as an extra numeral. To each cathode, an electrical lead from a respective lead pin 3 is passed through an aperture between one of the stacks of ceramic collars to join an ear of the cathode. The cathodes with their ears and a suitable length of lead may conveniently be made integrally from sheet material so that each lead is in the form of a tape continuous with an ear. Between its cathode ear and the base of the cup, the lead is located between the adjacent stack 9 on the one side and the side wall of the anode cup on the other. Connection is made between one of the lead pins and the metal cup and the anode meshes 12 and 12a are connected either to the cup 6 or to a separate lead pin. The tube is filled with a suitable gas at a pressure which, taking into account the separation between the several electrodes, will ensure that, when for a speciiied discharge current a specified potential difference is applied between the anode mesh 12 (and 12a) and any one of the cathodes, cathode glow covers substantially the whole of the numeral-shaped surface of the cathode in question on the side facing the top end of the envelope.

It is arranged, as will be more fully described below, that over a portion of their length between their junction with the respective cathode ears and passage through the apertures in the base of the cup 6, the electrical leads to the cathodes are so close to the wall of the cup on the one hand and the stack of the ceramic collars on the other that no discharge can occur at any of them at the specified potential d iiierence between anode and cathode. Beneath the base of the cup 6, normal shielding of the anode lead or leads together with the provision of the mica washer 8 serves to prevent discharge occurring between any leads at the base of the tube.

Referring now more particularly to FIG. 2, the manner in which the electrical leads are arranged will be described in greater detail. First it should be pointed out that the cathode glow at a glow discharge gap is located a short distance away from the cathode surface which is participating the discharge. The greater part of the anode to cathode potential drop is localised between the cathode glow and the cathode. During normal glow, that is, when the available cathode surface is not completely covered with the glow--the distance between the cathode surface and the glow is equal to the minimum sparking distance for discharge between the cathode and an anode electrode. This distance corresponds to the minimum of the Paschen curve for the gas and electrode materials in question wherein the sparking potential difference is plotted as a function of the product of gas pressure and gap length. If the gap distance is less than the minimum sparking distance, glow discharge cannot be initiated without an increase in voltage. In the case of an existing glow discharge on a neighbouring cathode or portion of the cathode electrode during the normal regime, the area of cathode glow is primarily a function of the glow discharge current and largely independent of voltage. When the whole of the available cathode surface is covered with glow, the effect of an increase in discharge current, for which an increased cathode-anode potential difference is required, is to bring the glow closer to the cathode. It is found that if a member of conducting or of insulating material is spaced from a first part of the cathode at a distance less than the minimum sparking distance, glow discharge at this first part can occur only at an increased cathode-anode voltage, while if the cathode-anode potential difference is such that glow discharge is being maintained at a neighbouring, second, cathode part with the glow spaced from the second part a distance greater than that between the first part and the member f conducting or insulating material, the glow will not spread to the first part (it being assumed, of course, that if the member is metallic its potential does not exceed the anode potential). This is the principle utilised in the present invention to prevent undesired glow discharge upon the electrical leads to the cathodes of the numeral indicator tube.

There are two possible causes of failure in a character display tube if glow discharge can occur on any of the leads. In the first place discharge from a glowing character may spread along the lead, which is obviously undesirable, while the second, and more serious cause of failure is for discharge to occur on a lead to a character which should be unilluminated and for the discharge then to spread along the lead onto the character; an undesired character then becomes illuminated. Both of these causes of failure are greatly reduced if, in accordanceV with the invention, normal glow discharge cannot be maintained on any lead by reason of its proximity to structural members of the tube.

In order to obtain the desire-d close spacing betweenl the electrical leads and the anode cup and the stacks 9 in the illustrated embodiments of the present invention, while allowing as much room as possible within the cup 6 for the numeral shaped cathodes, the wall of the cup 6 immediately adjacent a stack 9 is. displaced outwardly from the normal cylindrical shape of the remainder of the cup wall 4and the stacks 9 are positioned so that, but for these displaced portions, the cylindrical surface of the cup 6 would intersect them. At the same time these displacements Iof the side wall surface provide channels which assist in shielding the cathode leads from the field of other parts of the anode further away from which the -gap length to the leads is greater than the minimum sparking distance. Although the anode may be formed in one piece, in the embodiment illustrated in FIG. 2 the side wall is crut to provide clearance for the stack of washers 9 and a channel shaped member 13` is Welded over the resulting slot. The stack 9 is thus seated partially within the channel shaped member 13.

FIG. 2 also shorws a preferred arrangement of Ithe leads coming from out of the stack 9, six leads being shown. In `or-der to keep these leads in their proper position, two of the 4ceram-ic washers are provided with extension pieces 16 carrying slots, each lead 15 being placed in its own slot. At the base of the stack 9, as mentioned previously, the base of the cup 6 is apertured for passage of the leads. In the present embodiment the aperture is provided: in part by Vthe slo-tting of the side wall and the provision of the channels 13. A portion of the mica washer 8 is :also cut away to allow passage of the leads through to the base of the tube. To ensure accurate location of the channel pieces 13, its flanges are cut, one half of each flange being positioned against the inner surface of the wall of Icup 6 and the other on the out-er surface, as is also indicated in FIG. 3.

What we claim is:

An indicator Iglow discharge tube having a glass envelope with a base at one end, and a transparent part at the top end to permit viewing of glow ydischarge display within the tube, the base having lead pins sealed therethrough, and an electrode assembly supported by the lead pins, the electrode assembly including a metal cup with its base adjacent the base of the envelope and with longitudinal side walls along the length of the envelope, a plurality of sp-aced apart longitudinal stacks of insulating collars within the cup extending adjacent the cupl side walls, a set of cathodes having a plurality of diffeernt shapes, each cathode ybeing supported on said stacks across said tube and mounted between respective pairs of the collars so that the cathodes lie in respective superimposed planes, and an anode member extending across said. envelope over the set of cathodes, a plurality of electrical lead connections between respective said lead pins and the metal cup and anode mem-'ber and each cathode, the metal cup having Ilongitudinal channels in the side walls extending outwardly from Iand adjacent each stack of collars, each said cathode lead connection being disposed within said channels between the adjacent stack of collars and the cup side wall, 4said stack of collars including a collar hav- 5 6 ing an extension piece extending into said channel por- 2,906,906 9/ 1959 McCauley et a1. 313-2110 X tion, said extension piece having slots for reception of 2,990,061 6/ 1961 McCauley S13- 109.5 said lead connections along the side of said stack. 3,005,922 10/1961 Hart B13-109.5

References Cited by the Examiner 5 DAVID I. GALVIN, Primary Examiner.

UNITED STATES PATENTS GEORGE N. WESTBY, Examiner.

1,848,837 3/ 1932 Powers 317-99 D. E. SRAGOW, Assistant Examiner.

2,219,611 10/1940 Berghaus et al. 313--199 

